A drive sprocket and flexible tape combination has previously been disclosed in a number of prior patents. A steel belt with apertures to receive teeth on a sprocket has been disclosed in U.S. Pat. No. 239,114 and a laminated belt of plastic with apertures to receive the sprocket teeth has been disclosed in U.S. Pat. No. 3,577,794. Plastic belts with apertures therein have been suggested for use in closure operators, such as garage door operators, in U.S. Pat. Nos. 3,252,503 and 4,414,778. Further, such a tape has been disclosed in U.S. Pat. No. 4,520,684.
For over one hundred years, such sprockets have had a circular periphery under the assumption that the tape was capable of deforming to a circular arc and wrapping around a part of such periphery. In the latter patent, there was disclosed a plastic tape which was sufficiently stiff that it could transmit compression as well as tension forces so long as it was guided in a longitudinal channel. However, it has been discovered that the tape is more flexible at each aperture than it is in the areas between apertures. This means that in wrapping around the sprocket, the tape tends to bend more at the connecting areas laterally adjacent the apertures than at the web areas, which are those portions between longitudinally adjacent apertures. This has been found to cause the tape to tend to work its way radially off the sprocket teeth under load on the tape, and to cause the tape to be worn at the apertures.